Dust storms in China: a case studyof dust storm variationand dust characteristicsQ. Feng Æ K.N. Endo Æ G.D. Cheng

Abstract The paper discusses the nature of duststorms, which have inherent environmental im-plications. The physical, chemical and mineralog-ical properties of dust sediments collected inKashi, Taklimakan desert, Kunlun mountains,Donghuang, Lanzhou, Ningxia, Xi’an, Inner Mon-golia and Beijing from 1990 to 1994 were studied.The texture of most aeolian deposits ranges fromsilty clay to clay loam with median particlediameters (Mds) generally between 5 and 63 lm;similar to the loess of central China and the silt/fine sand in western and northern China. The dustsediments were characterized by a predominanceof SiO2 and Al2O3 and a high amount of K2O withmolar ratios for SiO2/Al2O3 and K2O/SiO2 from5.17 to 8.43 and 0.009 to 0.0368 respectively. Thetriple peak spectrum is the main form of massconcentration in a clear sky. In a dust storm itshows as a single peak, with quartz, feldspar,chlorite, illite, calcite and dolomite beingthe dominant minerals. The physical, chemical and

mineralogical properties of the present atmosphericdust are similar to those of wind-blown soils inwestern and central China. The results suggest thataeolian deposits and the fine-grained fractions ofdust sediments collected in northern China aremainly soils transported from the arid and semi-aridregions of China and Mongolia by the prevailingwinds.

Resume L’article discute de la nature des tempetesde poussieres, aux consequences importantes surl’environnement. Les caracteristiques physiques,chimiques et mineralogiques des sediments detempetes de poussieres preleves a Kashi, dans ledesert de Taklimakan, les montagnes de Kunlun, aDonghuang, Lanzhou, Ningxia, Xi’an, en Mongolieinterieure et a Pekin de 1990 a 1994 ont ete etu-diees. La texture de la plupart des depots eoliensvarie des argiles silteuses aux limons argileux. Lacourbe granulometrique presente une valeurmediane generalement comprise entre 5 et 63 lmargileux. Les caracteristiques physiques, chimiquesetrises par une predominance de SiO2 et de Al2O3

et une forte teneur en K2O avec des rapports SiO2/Al2O3 de 5,17 a 8,43 et des rapports K2O/SiO2 de0,009 a 0,0368. Un spectre a trois pics estcaracteristique d’un ciel clair. Dans une tempetede poussieres le spectre presente un seul pic avecquartz, feldspath, chlorite, illite, calcite et dolomitecomme mineraux preponderants. Les caracteris-tiques physiques, chimiques et mineralogiques dela poussiere atmospherique sont semblables acelles des sols souffles par le vent dans la Chine del’ouest et du centre. Les resultats de l’etude sug-gerent que les depots eoliens et les fractions finesdes sediments preleves dans la Chine du nord sontprincipalement des sols transportes de regionsarides et semi-arides de Chine et Mongolie par lesvents dominants.

Keywords Dust storms Æ Aeolian deposits ÆLoess Æ Silt Æ China

Mots cles Tempetes de poussieres Æ Depotseoliens Æ Loess Æ Taille de particule Æ Chine

Received: 9 October 2000 / Accepted: 4 September 2001Published online: 18 December 2001ª Springer-Verlag 2001

Q. Feng (&) Æ G.D. ChengCold and Arid Regions Environmentaland Engineering Research Institute,Chinese Academy of Sciences,260 West Donggang Road,730000 Lanzhou, China

K.N. EndoDepartment of Geosystem Sciences,College of Humanities and Sciences,Nihon University, 3-25-40, Sakurajosui Setagaya-ku,156-8550 Tokyo, Japan

Present address: Q. FengDepartment of Geosciences System,College of Humanities and Sciences,Nihon University, 3-25-40, Sakurajosui Setagaya-ku156-8550 Tokyo, Japane-mail: fengqi@chs.nihon-u.ac.jpTel.:+81-03-53768696Fax: +81-03-53768696

DOI 10.1007/s10064-001-0145-y Bull Eng Geol Env (2002) 61:253–261 253

Introduction

In this study a dust storm is defined as having an in-stantaneous wind velocity of >17 m/s and a sky visibilityof <500 m. Such storms are common phenomena whichoccur with great frequency and magnitude over the aridand semi-arid regions of the earth’s land surface (Yaalonand Ganor 1973; Yaalon and Dan 1974; Goudie 1978).Desert dust is often transported over hundreds of kilo-metres and much of the finest material is carried overthousands of kilometres. It is estimated that wind-blowndust transported from deserts amounts to 5·108 t annually(Naruse et al. 1986). The dust originates; from the majordeserts of the world; these arid and surrounding semi-aridlands covering 4.33·107 km2 or 36% of the earth’s landsurface (Meigs 1953). The most severe dust storms whichtransport particles over thousands of kilometres begin inregions with extensive deserts, such as the Sahara andnorthern and western parts of China (Pewe 1981; Yanget al. 1981). Evidence from modern grain-size measure-ments and dust storm observations indicates that the dusthas been transported mainly from the north and northwestarid and semi-arid areas of the Loess Plateau. The EastAsian winter monsoon circulation is also an importantagent for dust transport (An et al. 1990; Zhang et al. 1994,1999). However, dust transportation, its composition andpatterns are still not clear. The study reported here wasundertaken to analyse the deposition characteristics ofdust in modern times. In addition, the physical, chemicaland mineralogical characteristics of the aerosols and air-fall sediments collected in several places were studied inorder to provide statistical information for further re-search.During the period from March 1990 to May 1994 two de-position events occurred in eastern China, when mineraldust was recorded at Kashi, Taklimakan desert, Kunlunmountains, Donghuang, Lanzhou, Ningxia, Xi’an, InnerMongolia and Beijing. The individual dates were 12 March1990 and 5 May 1993. The low deposition mass (up to0.10 g/m2) meant that the dust in the atmosphere wassufficient to influence areas as far away as Japan andwestern America where some fallout events were also re-corded. Both the dust storms considered in the study werestrong, i.e. the instantaneous wind velocity was higherthan 20 m/s and the sky visibility lower than 200 m.The dust material was sampled in standard depositionbuckets and air-dried. Grain-size analysis was carried outusing the scanning electron microscope (SEM) and mi-crographs randomly taken from various parts of the SEMsample, a method described by Smart and Tovery (1981).All particles on a micrograph were measured (400–1,400counts per sample) and percentages of grain size repre-sented as total counts in each size class. The mineralogicalcomposition of the material was analysed by X-ray dif-fractometry of both tube and sedimentation samples. The200 mg samples were oven-dried at 110 �C and thenheated at 950� C. The loss on ignition (LOI) was calculatedfrom the difference in weight between 110 and 950� C.After fusing the samples with Na2CO3, the amounts of SiO2

were determined gravimetrically. The amounts of Al2O3

and Fe2O3 were determined by the ferron method (Dav-enport 1949) and the CaO and MgO content by the atomicabsorption method. After digesting the samples with HF-H2SO4, the amounts of MnO were also determined by theatomic absorption method. The TiO2 and P2O5 were col-orimetrically determined and the K2O and Na2O obtainedby flame photometry (Inoue and Naruse 1987). To observethe optical characteristics of aerosol particles, a spectralactinometer from the USA was used, allowing the wholewave range of solar radiation intensity to be obtained. Theinstrument was located in the Yinchuan station of Ningxia.This paper presents the basic characteristics of the mate-rial transported over a long range and discusses criticalclimatological factors that influence the deposition of dustfrom north China.

Dust storm variations

Based on 1,100 records of dust storm events in China, thetemporal and spatial distributions of dust storm eventssince historic times are discussed. These were recorded asdust rain or dust haze, which usually consisted of dust andyellow fine sand, sometimes mixed with rain in a mud. Ingeneral, the thickness of the fallen dust varied from a fewmillimetres to several centimetres.The earliest dust event recorded is in 1,150 B.C. (Wang1963) but the information over the last 1,000 years is muchmore abundant than that from the earlier centuries (Anand Liu 1984). In this paper, 1,100 historical records ofdust fall events from 300 to 2,000 years A.D. were studied(excluding local dust storms). Some meteorologicalinformation is presented in the discussion of the temporaland spatial distribution of dust, its climatic backgroundand synoptic process as well as the origin of dust.

Spatial distribution

The locations in which dust falls were recorded in historictimes are shown in Fig. 1. Their distribution covers anarea from Xinjiang to the coast of East China Sea and fromInner Mongolia to south of the Chang Jiang River, occa-sionally reaching Fujian, Guangdong and Guangxi areas.The figure suggests that the main areas where dust fallsoccurred are very similar to the distribution of loess inChina (An et al. 1990). Three characteristics are apparent:(1) most dust storms are at high latitude, thus involvingmuch of China; (2) the weather conditions concentrated inseveral areas related to strong dust storms; and (3) themain dust storms occurred in or close to the larger deserts.The dust storms studied originated to the west of Kashi,Xinjiang, east of Yulin in the Shaanxi Province, north ofFuyun, northern Xinjiang, north of Hails, Inner Mongolia,south of Hotan, Xinjiang and in the area of Golmud,Qinhai and Wuqi, Shaanxi. The areas affected by dust

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254 Bull Eng Geol Env (2002) 61:253–261

storms in China are geographically widespread andinvolve some 40,000 km2. The main distribution directionis west to east, but detailed information suggests that thesouthern Xinjiang basin, Hexi Corridor and HelanMountains are important regions for dust storms (Zhang1984; Oyang 1991).Strong dust storms (instantaneous velocity >20 m/s; skyvisibility <200 m) occurred mainly in southern Xinjiang,between Donghuang and Lanzhou and in the HelanMountain area, which distributed material in a north-westerly direction. From the historic record, over 85% ofthe dust storms occurred here or in northern Xingjiangand Hetao, Inner Mongolia.As noted above, the dust storms mainly originated in ornear the seven larger deserts (Fig. 1): the Taklimakan de-sert, the Kumtag desert, deserts in the Qaidam Basin, theBadain Juran desert, the Tengger desert, the Qubqi desertand the areas surrounding the Mu Us sandy desert (Fenget al. 2000). In the Taklimakan area, dust storms occur onsome 30 to 39 days each year, compared with 15 to 18 daysannually in the Qaidam areas, 13 to 34 in the Badain Jurandesert areas, 14 in the areas around the Mu Us sandydesert and 37 to 58 in the area of Qubqi.

Temporal distribution

A study was also made of the years in which dust falls wererecorded (Fig. 2; Zhang 1980), including the number ofyears in different decades and variations in the frequencyof dust storms each year. From the historical records itwould appear that there were frequent occurrences of dustfalls between 1060 and 1090, 1160 and 1270, 1470 and 1560,1610 and 1700, 1820 and 1890, and 1997 and 2000, withonly rare occurrences noted in the other periods referred

to in Fig. 2. The result of simulation of the frequencyvariations in Fig. 2 shows that the frequency variationsbetter coincide with polynomial regression and the entireregression coefficient including linear, logarithmic, poly-nomial and exponential regression is over 0.4 (Table 1).Based on the 1,100 dust storms considered, it would ap-pear that the frequency of dust storms has increased withtime (Fig. 2), possibly associated with the increase in theregional population. Particularly in the last 200 years, thefrequency of dust storms has increased rapidly comparedwith past centuries and during the same period there hasbeen a population explosion in northern China (Xia andYang 1996). The frequency of these aeolian events mayindicate that the environment has deteriorated seriously inrecent times, leading to further land desertification.Although dust storms occur in different months of theyear, they are most common during the early summer.Based on the 1,100 dust storms studied, it appears that‘‘dust rain’’ events are concentrated in March to May andare particularly common in April when some 26% of theannual total is recorded. In the Taklimakan area, most ofthe dust storms occurred between April and May, with afew being reported in June and between October andJanuary. In southern Taklimakan, dust storms were re-corded for some 3 to 6 days per month between April andJune. In Lanzhou and Xi’an, the historical records indicatethat the phenomena occur mainly between March andMay. In Ningxia, 60% of the occurrences annually are inApril, 13.6% in March and 26.0% in May, with very few(0.4%) being reported at other times of the year. Innorthwest China, the main period of dust storms is be-tween April and May, the earliest being recorded on 6March and the latest on 12 July.In addition to these seasonal characteristics, diurnalvariations can also be recognised. In northern Shaanxi,19% of the dust storms occurred in the morning compared

Fig. 1Distribution, frequency andobservation locations of dustand loess in China. 1 Kumtagdesert; 2 deserts in QaidamBasin; 3 Badain Juran sanddesert; 4 Tengger sand desert;5 Qubqi desert; 6 Mu Us sandyland; 7 Hexi Corridor; 8 Helanmountains; 9 Taklimakan desert

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with 63% in the afternoon and 18% at night; similar pat-terns have been recorded in other areas. The longest duststorm was in the Hexi Corridor and lasted for 15 h, al-though the average maximum length is 8 h. The spatialand temporal distribution of these events suggests thatthey are associated with regional climatic factors, such astemperature, aridity, etc.

Dust storms and temperature

In order to investigate the relationship between dust stormevents and temperature/aridity, a study was made of thevariation in temperature in north China over the last500 years (Zhang 1980). A comparison between the meantemperature index and the frequency of dust storms showsa significant inverse correlation (Fig. 3) with a correlationcoefficient of –0.59 (P<0.001).The deviation of winter temperatures between the warmand cold periods is about 0.5 �C for the past 500 years innorth China (Zhang 1989). The mean frequency of coldperiods is 3.7 years per decade and 2.1 years per decade

for warm periods. Notable cold periods were recordedbetween 1621 and 1700 and between 1811 and 1900, withwarm periods being recorded between 1511 and 1620 andbetween 1720 and 1780. As can be seen from Figs. 2 and 3,most of the dust storm events in north China occurredduring cold periods. Although Zhu (1973) proved thatsome dust storm events occurred between 690 and 710 – awarm period for China – most of the dust falls wereconcentrated in periods of low temperature.A comparison of the frequency of dust storm events withthe humidity in China (35–40�N) for the last 2,000 years(Zhen 1973) shows that most of the high-frequency duststorms correspond with dry spells. This is consistent withLiu’s explanation that loess deposits behave as silt underdry climatic conditions (Liu 1964, 1982). It is of interest tonote that the years when dust storms were prominent wereoften those in which El Nino occurred – for example: (1) adust storm on 9 September 1952 may be linked with the ElNino event that occurred between August 1951 and April1952; (2) the dust storm event on 22 April 1977 followedthe El Nino of June 1976 to March 1977; (3) there was adust storm event on 28 April 1983 and an El Nino eventfrom September 1982 to September 1983; and (4) the dust

Fig. 2.Variations in dust fall frequen-cies in northern China from300 to 2,000 years A. D.

Fig. 3.Relationship between frequencyof dust falls (solid line) andtemperature (dotted line) inBeijing over the last 500 years

Table 1.Some regression functions and relationship indices of frequency variations for dust falls between 300 and 2,000 years A.D.

Kinds Regression functions Indices

Linear regression Y=0.0018x+0.1174 R2=0.2046Logarithmic regression Y=1.6681Ln(x)–9.327 R2=0.1611Polynomial regression Y=2E–06x2–0.0031x+2.5751 R2=0.2531Exponential regression Y=0.8323e0.0007x R2=0.2275

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storm on 5 May 1993 during the El Nino event of April toDecember of 1993.

Physical characteristics of dust falls

Based on the relationship between the particle size of air-borne dust and vertical distribution, the particle size oftropospheric dust at an attitude of 6 to 10 km ranged from1 to 100 lm and was characterised by a predominance ofairborne particles with a diameter of 1 to 50 lm (Table 2).On the other hand, the stratospheric aerosol particles witha diameter of <1 lm were dominant at an altitude of>10 km. Consequently, it was considered that the clayey tosilt fractions of the dust sediments accumulated in Chinaare mainly associated with aerosols that have moved in thetroposphere. The dust sediments also contained varyingamounts of sand fraction (14 to 65%). The dust samplesfrom Kashi and Lanzhou in particular had a wide range ofparticle sizes (Table 2). Most of the coarser fraction inthese dust sediments is associated with soil materials blownby the wind from adjacent environments. Table 2 showsthat the particle size of the main dust sediments rangesfrom 5 to 63 lm. The sample from the Taklimakan area waspoorly sorted with a median particle size (Mds) of 2 to200 lm, while the samples from the eastern areas weremoderately well sorted with an Mds of 0.2 to 100 lm (Zhuand Cheng 1994). The sample from Xi’an was obtained nearthe loess plateau and had an Mds of between 0.2 and 80 lm,somewhat smaller than the samples of loess from theplateau with an Mds ranging from 3 to 16 lm (Table 2).The grain size of the aerosol particles collected from a325 m tower in Beijing was generally less than 0.4 lm, butduring periods of dust storms the dominant grain size wasbetween 0.6 and 1 lm (Qian et al. 1995) while the Mds ofthe well-sorted aerosol material collected on the flat roof ofthe building (about 10 m high) was 3.9 lm (Table 2). Pye(1987) notes that the further the distance from the source,the smaller the value of the Mds of the soils and aerosols.The results of the study are in agreement with other workon the relationships between the diameter of aerosol par-ticles and the transport distance from their source(Middleton et al. 1986; Prospero et al. 1987). However, theparticle size distribution (Mds) and soil texture of the air

fall material may be influenced by the longitude, latitudeand altitude of the sampling site and probably the seasonand meteorological conditions in China, as discussedbelow.

Chemical characteristics of dust

Table 3 presents the chemical components of the dust fallsstudied. As can be seen in the table, the material is char-acterised by a predominance of SiO2 and Al2O3. The SiO2/Al2O3 molar ratios of the dust and loess were 5.17 to 8.43and 6.3 to 9.3 respectively (Table 3). The amount of K2O inthe dust was low (0.57 to 2.07%), being very similar to thatof the loess (1.43 to 3.09%). As seen from Table 3, the K2O/SiO2 molar (0.009 to 0.0368) was also very close to that ofthe loess and aeolian soils of China (0.013 to 0.04). Theseresults suggest that the aerosols and dust collected inChina are predominantly composed of fine soil particlestransported from the loess plateau, the Gobi desert andtheir surrounds.Based on the characteristics of eight chemical componentsof dust in China, two types can be identified. The Xi’andust was characterised by a high level of loss on ignitionand CaO, smaller proportions of K2O and greater amountsof Na2O compared with the Beijing type which has lowerlevels of loss on ignition and CaO (Table 3).The suspended matter in the air is composed of two parts:natural material including volcanic particles, salt from thesea and aeolian particles; and material originating fromindustry. The value of the relative concentration of acertain element X to ferrum metal (EFx) is a useful indexfor an analysis of the sources of suspended matter:

EFx¼½ðX=FeÞair�=½ðX=FeÞcrust� ð1Þ

where Fe is the ferrum metal; [(X/Fe) air] represents therelative concentration of certain elements (X) to Fe in theair; and [(X/Fe) crust] represents the relative concentra-tion of certain elements (X) to Fe in the crust. The criticalconcentration of certain elements (X) to Fe in the crust hasbeen taken from Liu (1985).The values of EFx for some areas of China are given inTable 4. This shows that the variations in the EFx of most

Table 2Particle size distributions for dust falls in China in 1994. Mds Median particle diameters; So sorting coefficient of sample; Sk standard deviation;Kur kurtosis

Location Variations in Mds Mean Mds So Sk Kur(lm) (lm)

Kashi 0.2–200 23.21 1.27 0.756 3.802Kunlun mountains 1–80 23.13 1.17 1.319 5.557Taklimakan desert (Luntai) 2–200 93.54 1.43 0.117 2.316Donghuang 2–50 17.49 0.52 2.398 7.963Lanzhou 0.3–100 17.12 1.55 0.397 3.960Xi’an 0.2–80 20.00 0.85 0.966 4.480Ningxia (Yinchuan) 0.4–80 20.73 1.81 0.291 1.898Inner Mongolia (Xilin Hot) 0.3–80 10.15 1.08 1.031 2.878Beijing 0.2–50 3.97 0.34 1.176 8.693

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elements in Kashi, the Kunlun mountains, Tarim basin andDonghuang are the same while the concentration of most ofthe elements in the air is similar to their concentration inthe crust and generally close to 1. The high EFx value of Cais the result of a locally high proportion of Ca in the topsoil,while the elevated EFx value for Pb in Donghuang isprobably associated with the air pollution in an area wheretourism results in a greater population density. Generally,the factor of EFx in the dust sediments of most of the desertareas was lower than 10 compared with 1 in the other re-gions. The results show that the main elements suspendedin the air are fine sands and clays with a similar distributionto that of the soils found in the desert areas (Table 4); e.g. aCu of 23.76 in Lanzhou, 18.45 in Xi’an, 24.00 in InnerMongolia and 25.13 in Beijing; a Zn of 54.38 in Lanzhou,24.12 in Ningxia, 63.42 in Inner Mongolia and 79.34 inBeijing; and a Pb of 42.13 in Lanzhou, 13.74 in Xi’an, 35.11in Inner Mongolia and 78.12 in Beijing. The above highvalues of EFx in suspension may be the result of an in-creased proportion of clay matter, possibly associated withincreased transportation distances and/or regional pollu-tion (industrial particles) which could account for the highEFx value of Cu, Zn and Pb.

Mineralogical characteristicsof dust

The mineralogical content of the dust can represent thesurrounding source environment or the aeolian condi-tions. In the desert region, the X-ray diffractogramsindicated a predominance of quartz, feldspar, chlorite, il-lite, calcite, dolomite, gypsum and zeolite, with some 15 to30% organic (spore and pollen) and non-organic matter(Table 5). The mineral content of the dust was similar; thecoarse dust consisting of quartz, feldspar and carboniccarbonate while the fine dust was characterised by micaand clay minerals (Table 5). The light minerals content ofthe fall material was high, accounting for 90% of the totalcompared with a heavy mineral content of only 5% in thefluvial and aeolian sediments.In western China (in the Tarim basin, for example), theunstable mineral content of the dust reached 45% and wascharacterised by hornblende, black mica and augite, whilethe more stable 55% was dominantly epidote, zoisite,muscovite and garnet with trace minerals includingtremolite and actinolite. The light minerals were generally

Table 4Elements of dust falls (mg/kg) in north China in 1994

Location Cu Zn Pb Ni Co Cr Mn Fe Ti Ca Mg K Na

Kashi 0.80 1.77 2.68 0.60 0.59 0.43 1.12 1.00 1.33 4.95 1.54 1.25 1.12Kunlun

mountains1.23 1.87 2.98 0.32 0.43 0.53 1.25 1.54 1.65 5.89 1.32 1.05 1.02

Taklimakandesert(Luntai)

0.56 1.89 3.67 0.56 0.78 0.33 1.12 12.00 1.78 5.65 1.65 1.25 1.74

Donghuang 0.73 1.93 17.00 0.67 0.6 0.70 1.10 11.00 1.36 4.89 1.91 1.21 0.87Lanzhou 23.76 54.38 42.13 0.79 0.75 1.10 0.84 1.00 0.77 2.19 0.71 0.59 0.37Xi’an 18.45 2.21 13.74 0.48 0.80 1.70 1.02 1.00 1.52 3.03 1.10 1.25 0.94Ningxia

(Yinchuan)8.77 24.12 9.00 0.76 0.78 0.87 0.94 1.00 1.23 3.58 1.59 0.93 1.19

InnerMongolia

(Xilin Hot)

24.00 63.42 35.11 1.00 0.80 0.80 1.00 1.00 1.39 2.32 1.00 1.23 0.90

Beijing 25.13 79.34 78.12 2.13 0.78 0.89 1.10 1.20 1.45 2.45 1.00 1.42 0.78

Table 3Chemical composition and physical properties of dust falls in China in 1994. LOI Loss on ignition

Locations LOI SiO2 Al2O3 Fe2O3 TiO2 MnO CaO MgO Na2O K2O P2O5 SiO2/Al2O3 K2O/SiO2

(%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%)

Kashi – 56.2 8.27 3.64 0.53 0.07 10.46 2.88 2.76 2.07 0.17 6.79 0.0368Kunlun

mountains– 61.3 8.18 4.90 0.47 0.07 9.8 2.78 2.75 1.34 0.20 7.49 0.0219

Taklimakandesert (Luntai)

– 77.21 10.17 2.20 0.38 0.05 2.65 2.87 12.52 1.73 0.22 7.59 0.0367

Donghuang 3.77 75.77 9.21 2.60 0.12 0.04 2.56 1.17 2.07 1.55 0.07 8.22 0.0205Lanzhou – 59.3 11.47 4.04 0.60 – 5.96 1.32 2.17 1.20 0.20 5.17 0.0203Xi’an 13.7 62.51 6.41 4.9 0.7 0.08 6.27 2.25 1.70 1.17 0.20 8.43 0.0187Ningxia

(Yinchuan)4.91 66.79 9.07 5.48 0.46 0.09 1.64 1.62 2.26 1.21 0.11 7.36 0.0153

InnerMongolia(Xilin Hot)

– 71.23 11.15 4.83 0.70 – 5.36 1.14 2.1 0.77 0.10 6.39 0.0109

Beijing 2.68 63.5 10.41 5.63 0.58 0.15 0.73 1.54 2.53 0.57 0.07 6.10 0.009

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quartz, feldspar and calcite while the carbonic carbonatecontent in the falls sediment may reach 5 to 15%.In eastern China, the unstable mineral content of the dustand surface sand is only 30% – lower than in westernChina – while the opaque metal mineral content in theeastern areas is some 1 to 2 times that in the western areas.The muscovite and hornblende contents in the fall sedi-ments are lower than in western China, but the epidotecontent is higher.A semi-quantitative estimate of the relative amount of thedominant clay minerals based on the intensity of theircharacteristic reflections is shown in Table 5. The majorclay minerals of the dust sediments consisted of quartz,feldspar, chlorite, illite, calcite, dolomite, diorite and zeo-lite. However, there were differences in their clay mineralcomposition. In addition to the quartz content, the Kashi,Donghuang, Ningxia and Beijing dust contained largeamounts of illite while notable amounts of calcite werefound in the Kashi and Xi’an dust. Large amounts of do-lomite were found in the Kashi, Donghuang and Kunlunmountains and the feldspar content was high for the InnerMongolia and Tarim dust.As the dust samples were only collected every 1 to 4 weeks,it is difficult to analyse the relationships between the claymineralogy of dust and the dominant clay minerals innorthern China. However, there were similarities betweenthe mineralogical characteristics of the dust and themineral composition of soils in north China, where duststorms frequently occurred under low atmospheric pres-sure during the study period. The major clay minerals ofthe soils in these areas consist of quartz, feldspar, chlorite,illite, calcite, dolomite and diorite.

Spectrum distributioncharacteristics

The aerosol spectrum of number concentration and massconcentration were observed in Ningxia (Yingchuan sta-tion); see Fig. 4. In this figure, parts a and c represent thebackground condition considered as clear sky while partsb and d represent dust storm weather; the mass concen-tration spectrum in parts a and b corresponding to the

number concentration spectrum in parts c and d. Thespectrum of background mass concentration showed as atriple peak type (Fig. 4a) with diameters of 0.67, 3.0 and7.7 lm respectively. The whole spectrum coincided withthe log-normal distribution through three correspondingpeak value diameters. The mass concentration spectrum indust storm weather shows a single peak type with a geo-metric mean diameter of 3.09 lm. Again the spectrumcoincided with the log-normal distribution (Fig. 4b). Inclear skies, the number concentration of the aerosol is verylow, only 12.6/cm3 (Fig. 4c). The diameter of the peakvalue is 0.67 lm and its distribution type typically appearsas the T-distribution. The proportion of sand dust parti-cles <1 lm is 85% and the total mass concentration is38.3 lg/m3. In dust storm weather, the number concen-

Fig. 4a–dNumber concentration spectrum and mass concentration spectrum ofaerosol at Yinchuan: diameter of peak value (D), number concentra-tion of aerosol (N) and total mass concentration (M) are in lm, n/cm3

and lg/m3 respectively. Particle concentration is assumed as 1 g/m3;to convert into actual mass of sand dust, multiply by 2.7. a Massconcentration spectrum for background (clear sky) weather; b massconcentration spectrum in a dust storm; c number concentrationspectrum for background (clear sky) weather; d number concentra-tion spectrum for dust storm weather

Table 5.X-ray diffractograms of dust falls in China in 1994 (%)

Locations Quartz Feldspar Chlorite Illite Calcite Dolomite Diorite Gypsum Zeolite

Kashi 39 11 8 13 13 10 5 - 3Kunlun mountains 34 12 8 9 11 9 6 2 3Taklimakan

desert (Luntai)45 16 10 8 15 7 6 3 5

Donghuang 32 9 8 14 9 12 6 - 3Lanzhou 27 7 7 9 7 4 - 6 -Xi’an 38 9 8 10 10 4 - 6 3Ningxia (Yinchuan) 43 13 7 12 7 4 5 6 3Inner Mongolia

(Xilin Hot)40 17 5 8 6 6 5 - 5

Beijing 35 8 15 21 8 5 - - 3

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tration of the aerosol increases to 345/cm3, the peak valueof the aerosol diameter is 1.1 lm, and its distribution canbe fitted with the log-normal distribution, with a geometricaverage diameter of 1.56 lm (Fig. 4d).As can be seen from Fig. 4, the number concentrationspectrum of aerosol in clear skies has a typical single peakand can be fitted by T-distribution. In these conditions,the peak value is comparatively stable, ranging from 0.64to 0.84 lm with variations in the topography and geo-graphical location (You et al. 1991). In contrast, the peakvalue of the number concentration spectrum increaseswith the intensity of the dust storm and has a log-normaldistribution. While the triple peak spectrum is the mainform of the mass concentration spectrum in clear skies, itshows as a single peak in dust storm weather (You et al.1991).

Conclusions

The paper gives information on the loess deposits in Chinaand particle size and chemical analyses of particles ob-tained from dust storms between 1990 and 1994. It isconcluded that:

1. The main sources of the airborne dust studied are thenorth-western deserts and areas of Inner Mongolia.

2. The dust storms are capable of transporting particlesover vast distances. From the physical and chemicalanalyses undertaken, it is considered that such dustmaterials eventually form the loess and similar depositsfound in China. This is probably an important con-tributor to soil formation, slope wash and stream sed-iments in eastern China and in the adjacent seas.

3. The dust storms usually occur during cold periods,particularly between March and April. Correlation be-tween the main dust storms and reported El Nino oc-currences suggest there may be a relationship betweenthese phenomena.

4. The occurrence of dust storms has significant envi-ronmental and health implications. Man’s continualencroachment into the areas around the deserts/semi-deserts is likely to exacerbate the potential for erosion.This, together with the possible changes in global cli-mate, could pose significant problems, not only inChina, but over much of the surrounding area.

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